The present invention relates to a fixing device for use in, for example, copying machines, laser printers and facsimiles and to an image forming apparatus using the fixing device.
Image forming apparatuses such as an electrophotographic color printer or a color copying machine are mounted with fixing devices. Among fixing devices, a fixing device shown in FIG. 7 has been known as one having small heat capacity in order to accomplish reduction in temperature rising time. The fixing device generally includes a heating roller 101, a pressurizing belt 102 in contact with the heating roller 101, and a pressing member 103 placed inside of the pressurizing belt 102 to press an inner (rear) surface of the pressurizing belt 102 toward the heating roller 101.
The pressing member 103, which is constituted of elastic materials such as silicone rubber, has a function to stretch the pressurizing belt 102 over the heating roller 101.
To reduce the sliding resistance of the pressurizing belt 102, it is commonly used to insert a slide member 104 between the pressing member 103 and the pressurizing belt 102, and to interpose an oil between the inner surface of the pressurizing belt 102 and the sliding surface of the slide member 104, wherein the oil is fed from an oil application felt 106.
The oil accumulates in an inlet N1 of a contact section in which the slide member 104 is brought into a pressure contact with the inner surface of the pressurizing belt 102. The contact section is formed along with formation of a nip section which is formed by the contact between the heating roller 101 and the pressurizing belt 102. This oil accumulation is caused by such a high pressure that the oil fails to enter into the nip formed between the slide member 104 and the pressurizing belt 102.
As shown in FIG. 8, the oil, which fails to enter into the contact section between the slide member 104 and the pressurizing belt 102 and accumulated in the inlet section N1, is pushed out in the direction of an arrow “A” toward both end sections of the slide member 104. The oil is pushed out over both the end sections of the slide member 104. Thereby, the oil is attached to the pressurizing belt 102 and transported in the state of being attached to the pressurizing belt 102. Then, the oil comes around an inner surface of the slide member 104 due to being blocked by an edge section 103a of the pressing member 103.
The oil, which has come around the inner surface of the slide member 104, swells the pressing member 103. This causes a change of pressure in the nip section away from desired pressure so that wrinkles are generated on paper when the paper passes through the nip section.
Moreover, torque of the device is increased due to shortage of oil since the oil flows out onto the inner surface of the slide member 104. Consequently, lifetime of the device is shortened.
Conventionally, in order to prevent oil leakage out of both end sections of the contact section, JP 2005-77872A has proposed that an oil-central-collecting member is placed downstream of the contact section in such a way as to come into contact with an inner surface of the pressurizing belt.
However, the collecting member does not directly regulate oil leakage in the inlet section. Besides, the oil centrally collected by the collecting member is leveled by being rubbed against an oil coating member. Therefore, the collecting member has little effect on the prevention of oil leakage at both the ends of the inlet section.
JP 2002-372881A has proposed that oil is applied to a central portion only. This has some effect of suppressing the amount of oil overflowed to outside from the ends of the slide member, but no effect on oil leakage which has overflowed to the outside and come around the inner surface of the slide member.
JP 2005-3781A has also proposed that extrusions and indentions are spirally provided on an inner surface of belt so that oil is guided to the inside direction to prevent oil leakage when the belt rubs against a slide member. However, the belt is weak in binding force on oil, particularly in the inlet section. Therefore, this proposal has small effect on suppressing oil leakage to the outside of the ends of the slide member.
In any of the above-mentioned conventional devices, it is impossible to expect to functionally prevent the oil from leaking to the outside over ends of the slide member, from coming around the inner surface of the slide member and from swelling the pressing member.